Answer: If you wish to display the payment methods your store accepts within your store's footer, click the Footer bottom section and enable the Show payment icons checkbox.
Example:
These payment options cannot be edited through your theme, but rather through your Shopify admin. To do this:
Step 1: Within your Shopify admin, go to Settings.
Step 2: Select Payments.
Step 3: Under Payment providers, add your desired payment methods.
Visit Shopify's help center for more information on Shopify Payments.
Note: Shopify have their own article here: Add Credit Card Icons